Sensitivity of Peanut to Timing of Heat Stress during Reproductive Development

Peanut ( Arachis hypogaea L.) crops grown in the semi‐arid tropics are commonly exposed to damaging hot temperatures of above 40°C. The objectives of this research were to identify the time(s) during reproductive development when hot days reduce yield, and to examine relations between flower production and sensitivity to heat stress. At start of flower bud initiation (21 d after planting, DAP) plants of the cvs ICGV 86015 and ICGV 87282 were grown either at 28/22°C (optimum temperature, OT) or at 38/22°C (high temperature, HT) or were reciprocally transferred at 3‐d intervals between the OT to HT regimes and vice versa, until 46 DAP. Transferred plants remained in the new temperature regime for 6 d before being returned to their original regime. All plants were harvested at 67 DAP. In cv. ICGV 86015, transfers between 6 d before and 15 d after flowering (DAF) significantly ( P < 0.001) affected total number of pegs (i.e., pegs and pods) and reproductive (peg and pod) dry weight, with the greatest effect occurring at 9 DAF. In cv. ICGV 87282, number of pegs and reproductive dry weights were also significantly reduced by transfers at 9 and 12 DAF. Heat stress had no effect on flower production or the proportion of pegs forming pods, but did significantly reduce the proportion of flowers producing pegs. Data presented suggest that it is heat stress during floral bud development that determines peg number.